This invention relates generally to an improved multi-colored display device, and in particular to an improved multi-colored display device including at least two layered liquid crystal display cells.
Conventional means for providing a colored display in a conventional liquid crystal display device includes employing the DAP effect wherein two polarizing plates and a liquid crystal material of the homeotropic type are used. The vertical orientation of the liquid crystal material is altered as the voltage impressed across the cell is changed and the color is produced by the birefringence of the liquid crystal due to change in the orientation of the liquid crystal material. In a guest-host (GH) type liquid crystal display dyes are included in the liquid crystal material and a color is produced due to the dye property of absorbing light having a certain wavelength. In a liquid crystal display cell of the twisted nematic (TN) type, colored polarizing plates are employed.
It is difficult to provide a desirable colored display by using the DAP effect since the color variation is large due to its dependency on thickness of the liquid crystal layer, the voltage dependency is high and the color varies with differing angles of observation. In addition, display cells based on the GH effect or the TN type liquid crystal with colored polarizing plates provides colored displays limited to a single color. In addition, in these systems the display is not distinctly shown due to low contrast ratio. Accordingly, it is desirable to provide a colored liquid crystal display device of sufficient contrast and offering more than a single color combination.